Does anyone know how to install taller aerobar spacers that are compatible with the original aerobars? Or perhaps angled spacers for a better fit?

Yeah that looks bad, looks like half of the stem would clamp on nothing.
1. https://www.aliexpress.com/item/1005005627177754.html. That might work. Never used one, so check the diameters, but in principle, it should work?
2. A ghetto version would be to epoxy back a piece of the steerer on top of the steerer, then use the longest expander plug you can fit / find, so as to spread forces as far down the steerer as possible. There's a decent chance the epoxy bond would snap when you hit a pothole, i really dont know how much force steerers absorb, and how much they deform. There's a reason most catastrophic failures tend to happen in this area. Specialized recalled an entire model because of a fuck up there.
3. The easy way out is indeed to get a new fork.

I think 1&2 are worth exploring, unless you plan to ride the bike a tremedous amount and on sketchy terrain. Most TT bikes never see much elevation change, or sprints, so the demands on them are lower than on road bikes.

Thank you so much for your help! What an idiot I am…
I ordered a new fork to be very safe 😄 let‘s hope I will get it right this time

Hi guys, anyone had a problem with the stem? I mean - I screwed the side screws of the stem to 5NM and it is just so wobbly, the wheel does not turn with the rest of the cockpit. Do you think it is safe to put more than 5NM or what else can I do to fix it?

I have nearly the same problem - I installed everything with the Nm that VB told me and it looks good until I put pressure on the stem and it gets loose.
Maybe anyone can check  if the order of the installation steps from VB is right:

- tighten stem screws  to 5Nm
- tighten expander to 8Nm
- attach top cap and tighten front stem screws with 5Nm
- tighten top cap screw with 5Nm

I already tried a longer expander but didn‘t help either.

Happy for any help and tips!